1b.Approach (from AD-416):
To attain the first objective, we will correlate mitochondrial functional variation with catfish feed efficiency and identify and determine the role of specific genes and gene products (peptides and proteins) involved in controlling growth in catfish. For the second objective, we will construct a catfish microarray targeted toward immune function, characterize functional genetic variation in resistant vs. susceptible channel catfish, and characterize the effect of prebiotic administration on catfish immune function. For the third objective we will induce early maturation in channel catfish and blue catfish through compressed annual temperature cycles, increase ovulation and fertilization efficiency for production of blue X channel F1 hybrid catfish, and establish a technique for spematogonial transplantation between blue and channel catfish. For the fourth objective we will enhance and integrate genetic and physical maps, and identify quantitative trait loci associated with superior production traits, especially carcass traits and survivability to E. ictaluri infection. For the fifth objective, we will produce a line of select channel catfish based on multi-trait selection within a commercial composite population, produce a line of select blue catfish based on males that produce hybrid offspring with superior growth and carcass yield, and produce male channel and blue catfish which have a YY sex chromosome complement for all male catfish production.

3.Progress Report:
Consistent, superior performance of hybrid catfish and increased availability of hybrid catfish fry have contributed to increased levels of hybrid catfish production. Eight commercial hatcheries produce over 150 million hybrid catfish fry in 2012, an increase of 25 to 30 million fish from the previous year. The increased production is due in large part to technology transfer by ARS scientists at the Catfish Genetics Research Unit in Stoneville, MS. The scientists trained producers in the handling and preparing of broodfish, hormone delivery methods, and improved hatchery management procedures through on-site training, visits and consultation.

Protocols and procedures were developed that improve production efficiency and reduce the cost of hybrid catfish fry production in commercial catfish hatcheries. ARS scientists at Stoneville, MS, determined the minimum effective salmon gonadotropin releasing hormone (OvaRH) to stimulate final maturation and ovulation in channel catfish. This hormone is under Investigational New Animal Drug exemption, and four hatcheries participated to evaluate the efficacy of this hormone under commercial production conditions. The increased potency of this hormone enabled the fish to respond at lower dose and reduce the cost of hormone injections by 50 percent in hatchery production.

The estimated heritability of growth and filet yield in a pedigreed population of channel catfish was moderate, but heritability for resistance to infection by Edwardsiella ictaluri was very low. Selection for growth and filet yield continues in this population.

4.Accomplishments
1.
Evaluation of channel x blue and purebred channel catfish performance from 4 commercial farms. Channel x blue hybrid catfish production and use by the catfish industry have increased substantially in the last 3 to 5 years. ARS scientists with the Catfish Genetics Research Unit in Stoneville, MS, established non-funded cooperative agreements with the 4 largest producers of hybrid catfish in the U.S. to determine the effects of channel catfish strain, and female within strain, on hybrid offspring growth and carcass yield. In addition, purebred catfish from the same females will be evaluated for growth and carcass yield. This project was developed at the request of the producers and will provide information to determine if certain strains produce superior hybrid offspring, how much of differences in offspring performance are due to differences individual female parent, and if purebred channel offspring performance is predictive of hybrid offspring performance. All of this information will be important to producers as they develop breeding plans to improve hybrid catfish performance.

2.
Estimation of genetic parameters for growth, enteric septicemia of catfish (ESC) resistance and carcass composition in channel catfish. Estimates of heritabilities, the proportion of phenotypic differences due to genetic variation, for economically important traits are required for efficient selective breeding to improve these traits in channel catfish. ARS scientists with the Catfish Genetics Research Unit (CGRU) in Stoneville, MS, coordinate efforts to evaluate growth, fillet yield and ESC resistance of channel catfish as part of the CGRU breeding program. Heritability for growth and fillet yield were moderately high (0.35 and 0.38, respectively) while heritability for survival to Edwardsiella ictaluri challenge was not different from zero. Breeding values were estimated and fish were selected for improved growth and fillet yield based on a selection index with equal weighting for growth and fillet yield. Selected fish are currently being spawned and progeny will continue to be evaluated and selected as part of a long term breeding program to improve important traits in channel catfish for ultimate release of improved germplasm to the industry.

3.
Production and evaluation of hybrid catfish from various strains of blue catfish. Little information is available on the effects of blue catfish germplasm on production traits of channel x blue hybrid catfish offspring. ARS scientists with the Catfish Genetics Research Unit in Stoneville, MS, have obtained blue catfish from several geographic sources (strains) and have initiated a program to determine the effects of blue catfish strain and individual within strain on hybrid offspring growth and fillet yield. Analysis of growth and carcass yield of hybrid offspring resulting from a series of matings between channel catfish females and blue catfish males revealed significant effects of individual male and female parent on offspring performance and that these effects were additive. This will improve the efficiency of parent selection because the effect of parent on offspring performance is consistent and does not depend on a specific combination of male and female parent. Based on results of these trials, blue catfish germplasm that produces superior performing hybrid offspring will be identified, selected for further improvements and released to the industry.

4.
Multiple spawning in ponds by channel catfish females. A common assumption in commercial catfish production has been that channel catfish females release their eggs once during the spawning season, which generally occurs from late April to early July. Therefore, most fertilized egg masses are assumed to be separate families, although the potential exists for paternal half-sibling families due to multiple spawning by males. ARS researchers at the Catfish Genetics Research Unit in Stoneville, MS, have used DNA fingerprinting of spawns collected from ponds to produce pedigreed families. The DNA analysis identified paternal half-sib families but also revealed that many catfish females spawned two or three three times in a season. These spawning events were usually a month apart and sometimes included a second spawning event with the same male. While multiple spawning events increase the information used to calculate the genetic potential of broodstock, breeders can unknowingly increase levels of inbreeding when randomly selecting spawns from communally stocked ponds.

5.
Regulators of feed efficiency in catfish. Molecular factors that control feed efficiency are not well understood in catfish. Therefore ARS scientists in Stoneville, MS, continued research to investigate mitochondrial respiratory chain enzyme activities and gene expression levels in low and high feed efficient (FE) families of catfish. Mitochondrial enzyme activities in the liver, muscle and intestine were lowered in low FE channel catfish. Also the mitochondrial NADH dehydrogenase subunit 1 gene, involved in controlling oxidative phosphorylation, was up-regulated in the liver and down-regulated in the muscle and intestine of the high FE family. These differences in gene expression and enzyme activities provide insight into the cellular mechanisms of fish with differences in growth rate and feed efficiency and may be useful as selection markers for fish that grow more efficiently.

6.
Evaluation of prebiotics and essential oils for improving catfish production. Losses to disease lead to significant losses in catfish production so practical approaches are needed to improve catfish immunity. ARS scientists at Stoneville, MS, had replaced up to 80% of fish meal in a catfish diet with a yeast-derived prebiotic and showed that neither weight gain, feed efficiency, nor susceptibility to Edwardsiella (E.) ictaluri infection were affected. New research in tanks showed that fish fed essential oils gained approximately 40% more weight compared to control fish. Two large scale pond trials with essential oils demonstrated no improvement in weight gain but there was evidence of an improvement in survival. Fish in tanks that were fed essential oils showed a significant increase in survival after E. ictaluri infection compared to fish not fed essential oils. These results point to the potential of essential oils in catfish diets to replace fish meal and also to improve immune responses.

7.
Evaluation of a vertebrate gonadotropin releasing hormone to induce ovulation in catfish. Induced ovulation and manual stripping of high quality eggs is critical for efficient production of blue x channel hybrid catfish, which exhibit superior production characteristics. ARS researchers at the Catfish Genetics Research Unit in Stoneville, MS, tested a synthetic gonadotropin releasing hormone (GnRH) that was based on the structure of chicken GnRH II. The synthetic GnRH performed as well as mammalian luteinizing hormone releasing hormone analog (LHRHa) which is currently used in commercial hybrid catfish production. The synthetic GnRH also demonstrated the potential for improved synchronization of ovulation and higher numbers of fry produced compared to LHRHa. Increased production of hybrid catfish fry will improve production efficiency in the U.S. catfish industry.

8.
The pH of stripped channel catfish eggs predicts hatching success of hybrid catfish embryos. The quality of eggs that are manually stripped from channel catfish is affected by variation in female maturity, hormone dose, age and physical stripping process. Variable egg quality often results in inconsistent and unpredictable production of hybrid catfish fry in hatcheries, but reliable predictors of egg quality do not exist in catfish hatcheries. Therefore ARS scientists at the Catfish Genetics Research Unit in Stoneville, MS, conducted hatching trials to evaluate pH of stripped channel catfish eggs as a predictor of hybrid embryo viability. Channel catfish stripped eggs of low pH (pH < 7.0) were suggestive of low egg quality - resulting in poor hatchability of hybrid fry. Stripped eggs with higher pH (pH > 7.6) resulted in consistently higher hatch of hybrid catfish fry. The application of simple pH measure of stripped eggs enables the farmer to either discard or separate low quality eggs to improve the hatching efficiency of hybrid catfish eggs.

9.
Holding hormone induced channel catfish suspended in individual mesh bags improves the efficiency of hybrid catfish fry production. The process of maturation and ovulation in channel catfish is not synchronized and hormone-induced fish are periodically crowded, captured and handled to observe for signs of ovulation. Repeated handling and stress can hinder maturation and ovulation, lower egg quality, and reduce performance of the progeny. ARS scientists at the Catfish Genetics Research Unit in Stoneville, MS, conducted spawning trials to compare the reproductive performance of hormone-induced channel catfish either suspended in soft mesh nylon bags or held communally in tanks. Stress (plasma cortisol) response was significantly lower in fish suspended in mesh bags compared to communally held fish. Ovulated eggs from females held in bags had a 5.6% higher hatching success compared to females held communally in tanks. This method of holding fish has improved the efficiency of hybrid catfish production and has been adopted by 6 of the 8 commercial hybrid catfish hatcheries.

10.
Pre-spawning carotenoid fortified diets improve reproductive traits of channel catfish and performance of subsequent progeny. Obtaining sufficient quantities of eggs for hybrid catfish production depends on the availability of fully mature, gravid channel catfish females. In order to determine nutritional aspects of egg development in catfish females, ARS scientists at the Catfish Genetics Research Unit in Stoneville, MS, conducted a 10 week pre-spawning feeding study with varying levels of Astaxanthin in a commercial catfish feed. Mature females that were fed a diet containing 50 parts per million (ppm) Astaxanthin resulted in higher percent of increased maturation (81% vs 64%) and a 6.6% increase in hatch compared to fish fed the control diet. The subsequent progeny of Astaxanthin-fed females had improved survival when exposed to pathogenic Edwardsiella ictaluri and reduced responses to lower dissolved oxygen stress under laboratory conditions. The results indicate Astaxanthin may be a useful pre-spawning feed additive that will increase hybrid embryo production and survival.

11.
Evaluation of processing yield in fish from nutrition studies. Diet composition can affect fillet yield and composition, traits that influence profit and product quality. ARS scientists with the Catfish Genetics Research Unit in Stoneville, MS, in cooperation with researchers from Mississippi State University and the University of Arkansas Pine Bluff (a 1890s institution), processed catfish from multiple studies to provide carcass quality measurements for a variety of experiments. The carcass data will help researchers determine the impact of altering diet composition on processing yield in order to identify diets that will improve production efficiency.

12.
Exposure of hybrid catfish embryos to calcium-deprived waters in the first 48 hours post-fertilization is detrimental to hatching success. Hybrid catfish production is a long and steady process that requires optimization of all processes in hatchery production. Most hatchery waters are supplied with soft geothermal waters that must be supplemented with continual injection of calcium chloride. Electrical or mechanical breakdown can result in calcium deprivation in hatchery waters. ARS scientists at Stoneville, MS, conducted hatching trials to evaluate the exposure of hybrid catfish eggs to calcium deprived waters at twelve sequential 8-hour periods during embryogenesis. Exposure of any 8-hour period in the first 48 hours post-fertilization reduced the hatching success of hybrid catfish eggs by 50 percent. The results demonstrated the importance of monitoring calcium hardness in hatching waters in hybrid catfish hatcheries.